1. Technical Field
The present invention relates to the construction of buildings such as large open span buildings and more particularly relates to composite floor systems and a novel design for joists used in such a floor system and installation of such joists.
2. Background Art
Composite floor systems have been employed in multi-story building construction for many years and improvements are constantly being sought, both in the materials used in the composite floor systems and the methodologies used to erect the buildings that incorporate composite floor systems. The development and sophistication of these structural systems has gradually extended to encompass many varieties of steel and concrete floor construction, the result of which has been to measurably reduce the cost of steel framing for multi-story buildings in the industry.
In the past, concrete and steel floor construction methods have included open-web steel joists placed in position spanning structural supports with a concrete slab poured on decking supported by the joists. Generally, an open-web steel joist is a joist in the form of a truss having horizontal top and bottom chords joined by a web comprising tension and compression members triangulating the space between the top and bottom chords.
While the chords may be of many shapes, typically, the top and bottom chords each comprise a pair of steel angle bars, the top chord angle bars being arranged with one leg of each bar extending horizontally outward at the top of the truss, and the other leg of each bar extending downwardly on opposite sides of the web. The bottom chord angle bars are arranged with one leg of each bottom chord angle bar extending horizontally laterally outward at the bottom of the truss, and the other leg of each bottom chord angle bar extending vertically upward on the opposite sides of the web. Decking for supporting the concrete slab is laid on and fastened to the horizontal leg of the top chord angle bars at the top of the joist, and a concrete slab is the poured on the decking. Using this typical construction methodology, there is no structural integration of the concrete slab to the joists and the slab and joists function as separate entities with the slab constituting a “dead load” on the joists without materially contributing to the strength of the overall structure.
In another construction method, the upper ends of the web members project upwardly above the upper horizontal legs of the top chord angle bar for anchorage in the concrete slab to form a composite slab and joist construction in which the slab may, to some extent, become a compression member sharing part of the load. It has been found that this type of construction does not obtain the full potential of a composite slab joist construction, and has certain disadvantages. For example, the effective anchorage is between the slab and the upper ends of the web members so that transfer of stress between the joists and the slab occurs only at the upper ends of the web members. Furthermore, the slab is necessarily placed above the level of the supporting structure for the joists. In addition, the decking is formed with slots to enable the web member to protrude into the concrete forming the composite section. This creates another problem, namely, that the slots must be exactly aligned along the length of the building and the joist must also be perfectly aligned.
Yet another construction method employs an open-web steel joist in the form of a truss having a web, a top chord and a bottom chord. The top chord comprises a pair of steel angle bars arranged with one leg of each of the angles extending horizontally outward from a position on the truss below the top of the truss, and the other leg of each angle extending upwardly to the same height on opposite sides of the web and terminating below the top of the web. Decking is laid on the horizontal legs of the top chord, and concrete is poured on the decking to embed the vertical legs of the top chord angle bars and the upper ends of the web in the concrete slab to create a composite floor structure. In this construction, the top chord is below the top of the web member and composite action is obtained primarily by embedding the portion of the web extending above the top of the top chord into the concrete slab.
It will be appreciated that the purposes of composite floor construction are to save considerable steel weight and cost, as well as to reduce depth and deflection. While many of these various methods for forming composite floor systems have enjoyed some commercial success in achieving the stated goals, there is a continual search for even more effective and efficient methods for constructing these composite floor systems.
In view of the foregoing, it should be appreciated that it would be desirable to provide additional methodologies for constructing various types of composite floor systems that are simpler and less expensive to install, using existing materials and components to the extent possible.